A desirable feature of polymer materials in many instances is an appearance of whiteness. For instance, it is often desired that fabrics manufactured from polyester fiber present the appearance of whiteness to the observer.
Unfortunately, native polyester fiber as manufactured has a yellowish appearance unacceptable to the observer.
At the present time, in order to improve the apparent whiteness in polyester materials, toners are incorporated into the polyester to hide the yellow color. Such toners usually have a visible absorption maximum in the range of 575 nm to 595 nm as measured in acetone.
Cobalt acetate is one of the most widely used toners in the industry to mask the yellow color of polymers. However, cobalt acetate has a number of disadvantages.
For instance, cobalt acetate toner materials tend to be unstable during storage as a result of temperature and humidity and undergo an undesirable color shift toward yellow. Hence, when high cobalt concentrations (70 ppm) are needed to mask the yellow color of some polymers there is a tendency to impart a gray color to the polymer.
Secondly, high cobalt concentrations are a concern to some regulatory agencies.
Thirdly, cobalt lowers polymer thermal stability and increases acetaldehyde formation in poly(ethylene terephthalate).
Lastly, cobalt has a strong tendency to form insoluble residues that collect on the interior walls of the reactor which leads to quality problems.
Thus, a real need is perceived to exist for a toner or dye which improves the apparent whiteness of polymers such as polyester which at the same time lacks the shortcomings that the are associated with prior art toners such as cobalt acetate.